Traditionally, and as shown in FIG. 1, a vibrator truck 1000 comprises a vehicle (also referred to as “mobile platform”) 1001 and a vibration assembly (also referred to as “shaker”) 1002 which are mobile relative to each other by a lift system assembly (also referred to as “ground-hugging assembly”).
The function of the vibration assembly is to apply, to the ground, a variable force (of the sinusoidal type for example) of predetermined nominal value. To this end, and referring to FIG. 2, the vibration assembly includes a vibrator part and a baseplate (also referred to as “support plate”) 210 for coupling to the ground. The baseplate 210 is used to transmit the vibrations generated by the vibrator part through the ground. In the shown example, the vibrator part includes a reaction mass 270, a drive piston 260, an upper plate 280 and stilt legs 225. The stilt legs, located between the upper plate 280 and the baseplate 210, are intended to more evenly distribute the pressure applied by the weight of the mobile platform onto the baseplate 210. The drive piston 260 guides the reaction mass 270 in a relative movement with respect to the baseplate 210 when the servo valve is operated. The vibrator part is thus used to generate a seismic vibration wave and to transmit it into the ground.
The ground-hugging assembly is fixed to the vibration assembly, and mounted to slide on the chassis 100 of the vehicle 1001:                firstly to place the vibration assembly on the ground or raise it. In other words, the ground-hugging assembly behaves like a lift system configured to lift the vibration assembly up (for moving the vehicle between two vibration locations) or down (for placing it on the ground, at a vibration location); and        secondly to transfer the weight of the mobile platform onto the baseplate 210 and the top plate 280, which thus applies a static pre-load in a direction along an axis 1, to increase the power of the vibration transmitted to the ground.        
In the example shown in FIG. 2, the lift system includes guide bushings 240 mounted in the chassis 100 of the vehicle in which lift (guide) columns 290 can slide, at least one footbase (also referred to as “beam”) 230 secured to the lower part of the guide columns 290 and more or less perpendicular to the lift (guide) columns 290, and lift cylinders 220 mounted between the chassis 100 and the footbase 230 to control the transfer of the weight of the vehicle on the vibration assembly.
More details concerning the known technique (described briefly above) can be found in U.S. Pat. No. 7,499,378, which is incorporated herein by reference. In particular, a description of elements 3, 4, 200, 251-255 and 258 is not given herein but can be found in the aforesaid US patent.
In the phase of lifting up or down the vibration assembly, i.e. when the vehicle weight is not transferred on the baseplate, the connection between the ground-hugging assembly (and more precisely the at least one footbase) and the vibration assembly is ensured by chains mounted in hose-like pieces of rubber, thus giving the vibration assembly a sufficient degree of movement to adapt to a ground which is rarely flat. In the up position and in the phase of lifting up or down the vibration assembly, the chains support the load of the vibration assembly and are therefore tensioned. In the down position, when at least a part of the vehicle weight is applied to the vibration assembly, the chains no longer support load and are therefore released (slackened).
The rubber hoses, or sheaths (sleeves), around the chains prevent links of the chains to knock against each other (i.e. prevent the clicking of the links) during vibration in the down position, and thereby avoid producing a noise resulting in pollution for the seismic acquisition (slackened chains down).
This known solution of chains with rubber hoses is reliable and adapted.
However, for vibrator trucks having a great peak force output (e.g. 60,000 lbf (i.e. 264 000 N) or more), there are sometimes breaks (failures) of the chain attachments, requiring replacement operations, or preventive maintenance. In both cases the implementation or withdrawal of chains is a complicated operation.
Sometimes, the forces applied to the chains distort the fixing nuts and it becomes even more difficult to replace the chains which might need new brackets to be welded.
Moreover the rubber hoses are not always completely effective and a noise resulting from the clicking of links is sometimes observed.